Astronomy Distinguished Alumni Colloquium

"Why the Invisible Reservoir of Gas Around Galaxies Counts in Galaxy Evolution"

Galaxies like the Milky Way are engaged in an evolving balancing act among gas supply, consumption, and removal. Many of the baryons involved in this cycle are in a phase that is difficult to observe directly -- diffuse, highly-ionized gas in the halo, aka the circumgalactic medium. In this talk I will present absorption-line observations of the CGM that help to reveal the physical and dynamical state of circumgalactic gas. I will show that under simple assumptions such as ionization equilibrium, the cool and warm phases of the CGM (T < 10^6 K) can account for most of the baryons purported to be missing from dark matter halos of both star-forming and passive galaxies with M_halo ~ 10^12. Yet, under these same assumptions, the cool (10^4 K) gas in the CGM is far from pressure equilibrium with a hot medium (10^6 K) that could provide hydrostatic support. I will present new (and future) survey data that will not only address several outstanding questions related to the CGM but will ultimately enable a more complete picture of both the CGM and the cosmic web surrounding it.

Jessica Werk is an Assistant Professor at University of Washington. She is an expert on gas in and around galaxies. She obtained a PhD in Astronomy from the University of Michigan in 2010.